- #36
yungman
- 5,755
- 292
rbj said:why not assume it has negative resistance?
the issue is, yung, that when that cap discharges, the energy stored in the cap ends up somewhere. where do you think it goes?
better clip on some heat sinks to the MOSFETs.
My name is Yungman or Alan
I am using an ideal case, there is no ohmic loss as a start to look at whether there is power involve in an ideal case.
For real case, you can use a MOSFET with very low output impedance to sink or source large current with very little heat. eg, if on channel resistance is 10mΩ, 1A only generate 10mV and power dissipation is very low even if charging a cap to 10V.
In computer, almost all circuits are MOSFETs, the biggest biggest problem is to charge and discharge the input and the line capacitance to achieve the logic level. Input capacitance and drive is THE single major issue of the speed limit. They get away with higher and higher speed inside the CPU only when they shrink to transistor down to lower the input capacitance. That's the reason they manage to run GHz inside the chip. But any external bus is still slow because of the trace and input capacitance need to be driven. The output has to be buffered over and over so the speed goes down. I want to see how driving a cap don't consume power.
Last edited: